Vulcanization mold and pneumatic tire manufactured with the mold

ABSTRACT

A vulcanization mold in which a blade has a blade proximal end portion, a blade distal end side thick portion expanded in a thicknesswise direction on the distal end side, and a blade connection portion that connects the portions to each other, is a vulcanization mold wherein a sweep area that is the difference where a cross sectional area of the blade connection portion is subtracted from an area from the blade distal end side thick portion to a mold surface with a width equal to a maximum width of a thickness of the blade distal end side thick portion in a cross sectional shape perpendicular to a tire widthwise direction of the blade is smaller at the blades in circumferential end portion side regions than at the blades in a circumferential central portion side region of the sector mold. Further, a pneumatic tire is manufactured using the vulcanization mold.

TECHNICAL FIELD

The present invention relates to a vulcanization mold for formingwidthwise grooves on a tire tread and a pneumatic tire manufactured withthe mold.

BACKGROUND ART

Widthwise grooves such as sipes provided so as to extend in a tirewidthwise direction on a tire tread contribute to drainage in additionto the expected edge effect.

However, when abrasion of the tread surface progresses as a result oftraveling, the rigidity of the tread part increases, and this degradesthe edge effect and, as the groove depth decreases, the drainage issometimes degraded to deteriorate the wet performance.

Thus, an example is available in which the width of the bottom portionof widthwise grooves of the tire tread is increased such that, even ifabrasion of the tread surface progresses, the edge effect and the wetperformance can be maintained (for example, refer to Patent Document 1).

PRIOR ART DOCUMENT Patent Documents

-   Patent Document 1: JP 2013-129327 A-   Patent Document 2: JP 2006-334872 A

In a pneumatic tire disclosed in Patent Document 1, a plurality of sipesare provided so as to extend in a tire widthwise direction on blockspartitioned by main grooves and transverse grooves of the tire tread.

The sipes include expanded bottom portion sipes having an expandedportion at a bottom portion thereof, and such expanded bottom portionsipes are provided substantially uniformly without being one-sided inthe circumferential direction on an outer circumferential face of thetire tread.

Normally, the tread part of a pneumatic tire is vulcanization moldedwith an annular mold of a vulcanization mold.

The annular mold is split into a plurality of sector molds in acircumferential direction, and the sector molds are moved in directionstoward the center and combined to clamp a raw tire on the inner side tovulcanization mold the raw tire (for example, refer to Patent Document2).

On a mold surface of the sector molds, blades that are thin plate-likemembers extending in a tire widthwise direction, which form sipes and soforth, are implanted.

Since a sipe is formed perpendicularly to the tread outer surface,namely, in such a manner as to cut in toward the tire center axis, ablade provided on the mold surface of a sector mold is implantedperpendicularly to the mold surface, namely, in such a manner as toprotrude toward the center axis when the sector molds are combinedannularly.

A blade for holding an expanded bottom portion sipe has a distal endside thick portion expanded in its thicknesswise direction on the distalend side thereof.

SUMMARY OF THE INVENTION [Underlying Problems to be Solved by theInvention]

Since sector molds are moved in directions toward the center andcombined to perform vulcanization molding, when mold opening is to beperformed after the vulcanization molding, the sector molds are moved inradial directions away from the center.

Accordingly, the protruding direction of each blade protrudingperpendicularly to the mold face of the sector mold is, in acircumferential central portion side region of the sector mold, asubstantially parallel direction to a direction in which the blade ispulled out from the tire tread at the time of mold opening (in a radialdirection away from the center of the sector mold). Thus, even a bladehaving a distal end side thick portion is easily pulled out from themold under low resistance because the distal end side thick portion ispulled out substantially in parallel to the protruding direction.

However, in regard to each blade in a circumferential end portion sideregion of the sector mold, the protruding direction is not parallel to adirection in which the blade is pulled out from the tire tread at thetime of mold opening but has some angle. Therefore, a blade having thedistal end side thick portion tends to be pulled out in a directionhaving the angle with respect to the protruding direction. Consequently,the blade is acted upon by comparatively high resistance and pullout ofthe blade from the mold is not easy, and in some cases, such a failureas missing of part of blocks or damage to a mold is liable to occur.

The present invention has been made taking such a point as justdescribed into consideration, and it is an object of the presentinvention to provide a vulcanization mold that is a mold includingblades having a distal end side thick portion and by which pullout fromthe mold is performed smoothly without causing any failure and apneumatic tire manufactured using the vulcanization mold.

Means to Solve the Problem

In order to achieve the object described above, according to the presentfirst invention, there is provided a vulcanization mold in which anannular mold for forming a tire tread of a pneumatic tire is split in acircumferential direction into a plurality of sector molds and thesector molds are each moved in directions toward the center and combinedwith each other to clamp a raw tire on the inner side to vulcanizationmold the raw tire,

each of the sector molds having blades implanted on a mold surfacethereof, the blades being thin plate-like members extending in a tirewidthwise direction and being used to form groove lines on the tiretread,

each of the blades having a blade proximal end portion to be embeddedinto the sector mold, a blade distal end side thick portion expanded ina thicknesswise direction on the distal end side, and a blade connectionportion that connects the blade proximal end portion and the bladedistal end side thick portion to each other, in which

a full length of a protruding side that protrudes from the sector moldof the blade connection portion of the blade is shorter at the blades inthe circumferential end portion side regions than at the blades in thecircumferential central portion side region of the sector mold.

The full length of the protruding side that protrudes from the sectormold of the blade connection portion of the blade (side protruding fromthe mold surface) indicates a degree of difficulty in pullout from themold, and as the full length of the protruding side of the bladeconnection portion decreases, the resistance at the time of pullout fromthe mold becomes lower, and the pullout from the mold becomes easier.

According to the configuration described above, by making the fulllength of the protruding side of the blade connection portion of theblade in the circumferential end portion side regions, which blade isnot easier in pullout from the mold than the blade in thecircumferential central portion side region of the sector mold, smallerthan the full length of the protruding side of the blade connectionportion of the blade in the circumferential central portion side region,pullout of the entire sector mold can be performed smoothly withoutcausing failure at the time of mold opening of the vulcanization mold.

A preferred embodiment of the present invention is the vulcanizationmold, in which

a multiplication value obtained by multiplying a sweep area that is adifference where a cross sectional area of the blade connection portionis subtracted from an area from the blade distal end side thick portionto the mold surface with a width equal to a maximum width of a thicknessof the blade distal end side thick portion in a cross sectional shapeperpendicular to the tire widthwise direction of the blade by a fulllength of a protruding side of the blade connection portion is smallerat the blades in the circumferential end portion side regions than atthe blades in the circumferential central portion side region of thesector mold.

The sweep area that is the difference where a cross sectional area ofthe blade connection portion is subtracted from an area from the bladedistal end side thick portion to the mold surface with a width equal toa maximum width of a thickness of the blade distal end side thickportion in a cross sectional shape perpendicular to the tire widthwisedirection of the blade indicates a degree of difficulty in pullout fromthe mold, and as the sweep area decreases, pullout from the mold becomeseasier.

Therefore, the multiplication value obtained by multiplying the fulllength of the protruding side of the blade connection portion by thesweep area indicates a degree of difficulty in pullout from the mold,and as the multiplication value decreases, pullout from the mold becomeseasier.

According to the configuration described above, by making themultiplication value of the sweep area in the circumferential directionend portion side regions and the full length of the protruding side ofthe blade connection portion, which blade is less easier in pullout fromthe mold than the blade in the central portion side region of the sectormold, lower than the multiplication value of the sweep area in thecentral portion side region and the full length of the protruding sideof the blade connection portion, pullout of the entire sector mold canbe performed smoothly without causing failure at the time of moldopening of the vulcanization mold.

The present second invention is a pneumatic tire manufactured using thevulcanization mold.

According to this configuration, the pneumatic tire manufactured usingthe vulcanization mold makes pullout from the mold at the time of moldopening smooth, and the manufacture efficiency can be increased withoutcausing mold pullout failure such as missing of part of blocks.

Effects of the Invention

According to the present invention, by making the full length of theprotruding side of the blade connection portion of the blade in thecircumferential end portion side regions, which blade is less easier inpullout from the mold than the blade in the circumferential centralportion side region of the sector mold, shorter than the full length ofthe protruding side of the blade connection portion of the blade in thecircumferential central portion side region, pullout of the entiresector mold can be performed smoothly without causing failure at thetime of mold opening of the vulcanization mold.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general schematic view of a vulcanization mold according toan embodiment of the present invention.

FIG. 2 is a perspective view of one sector of the vulcanization mold.

FIG. 3 is a development view of a tread surface of a tire tread moldedwith a sector mold.

FIG. 4 is a cross sectional view perpendicular to a tire widthwisedirection of the sector mold of the vulcanization mold.

FIG. 5 is an enlarged sectional view of a blade in a circumferentialcentral portion side region C.

FIG. 6 is an enlarged sectional view of a blade in a circumferential endportion side region E.

FIG. 7 is a cross sectional view perpendicular to a tire widthwisedirection of a sector mold of a vulcanization mold according to anotherembodiment.

FIG. 8 is an enlarged sectional view of a blade in a circumferentialcentral portion side region C.

FIG. 9 is an enlarged sectional view of a blade in a circumferential endportion side region E.

MODES FOR CARRYING OUT THE INVENTION

In the following, an embodiment according to the present invention isdescribed with reference to FIGS. 1 to 6.

A vulcanization mold 1 for a tire according to the present embodiment issplit into a plurality of sectors (in the present embodiment, into ninesectors) in a circumferential direction as depicted in FIG. 1, and aholder 2 of each sector holds, on the inner circumference side thereof,a sector mold 3 for molding the tread part of a tire.

The sector mold 3 itself held by the holder 2 is a mold of the splitmold type configured from a combination of a plurality of split molds 4,and each holder 2 holds a plurality of split molds 4 split in acircumferential direction to configure the sector mold 3.

Each holder 2 is slidably movable in a diametrical direction, and whenall holders 2 slidably move in a centrifugal direction at the same time,the vulcanization mold 1 is opened to a large diameter concentric circleand a raw tire can be set to the inner side center of the vulcanizationmold 1.

Then, all the holders 2 are slidably moved toward the center all at oncewith a raw tire placed in the inside thereof to close the vulcanizationmold 1 to configure an annular mold as depicted in FIG. 1, andvulcanization molding of the raw tire on the inner side is performed.

FIG. 2 is a perspective view of the holder 2 of one sector and aplurality of split molds 4 held by the holder 2.

Circumferential ridges 5 extending in a tire circumferential directionare formed so as to protrude from a mold surface 4 f of the split mold4, and on the sector mold 3 in which such split molds 4 are combined,five continuous circumferential ridges 5 are formed in a tire widthwisedirection so as to form circumferential grooves therebetween.

On the mold surface 4 f of the sector mold 3, blades 6 and 7 that arethin plate-like members are implanted between adjacent ones of thecircumferential ridges 5 such that they extend in a rather inclinedrelationship in the tire widthwise direction.

The plurality of blades 6 and 7 are arrayed substantially uniformly inthe tire circumferential direction and in parallel to each other.

FIG. 3 is a development view of the tread surface of a tire tread 21 ofa manufactured pneumatic tire 20 molded by a sector mold 3.

Five tire circumferential grooves 25 are formed in the tirecircumferential direction with the circumferential ridges 5 of thesector mold 3 such that they are arrayed in the tire widthwisedirection.

On land portions between adjacent ones of the tire circumferentialgrooves 25, sipes 26 and 27 that are widthwise grooves are formed withthe blades 6 and 7 of the sector mold 3 such that they communicate thetire circumferential grooves 25 with each other.

FIG. 4 is a sectional view of the sector mold 3 perpendicular to thetire widthwise direction.

Referring to FIG. 4, although the blades 6 in a circumferential centralportion side region C and the blades 7 in circumferential end portionside regions E protrude perpendicularly from the mold surface 4 f, theyare different in shape from each other.

It is to be noted that the circumferential central portion side region Chas a region width of approximately 50% of the circumferential totalregion width of the sector mold 3 and regions on the opposite sides ofthe circumferential central portion side region C are circumferentialend portion side regions E.

When mold opening is to be performed, each sector mold 3 is moved in aradial direction R away from the center.

In particular, the radial direction R is a direction in which, at thetime of mold opening, the blades 6 and 7 are pulled out from the tiretread 21.

The protruding direction of each of the blades 6 protrudingperpendicularly to the mold surface 4 f in the circumferential centralportion side region C is substantially parallel to the radial directionR in which the blade is pulled out from the tire tread at the time ofmold opening, and even though the blade 6 has a blade distal end sidethick portion 6 c, the blade distal end side thick portion 6 c is pulledout in parallel to the protruding direction. Therefore, the resistanceis low and the blade 6 can be pulled out readily from the mold.

On the other hand, the protruding direction of each of the blades 7 ineach circumferential end portion side region E of the sector mold 3 isnot parallel to the radial direction R in which the blade 7 is pulledout from the tire tread at the time of mold opening and has a certainangle. Therefore, the blade 7 having a blade distal end side thickportion 7 c is acted upon by high resistance because the blade distalend side thick portion 7 c tends to be pulled out in the direction Rhaving an angle with respect to the protruding direction. Consequently,pullout of the blade 7 from the mold is not easy in comparison with thatof the blade 6 in the circumferential central portion side region C.

Therefore, the blades 6 in the circumferential central portion sideregion C and the blades 7 in the circumferential end portion sideregions E are different in shape from each other.

An enlarged sectional view of a blade 6 in the circumferential centralportion side region C is depicted in FIG. 5.

The blade 6 has a blade proximal end portion 6 a to be embedded into thesector mold 3, a blade distal end side thick portion 6 c expanded in thethicknesswise direction on the distal end side and a blade connectionportion 6 b that connects the blade proximal end portion 6 a and theblade distal end side thick portion 6 c to each other.

The blade proximal end portion 6 a and the blade connection portion 6 bhave a form of a thin plate of a fixed plate thickness, and while theblade proximal end portion 6 a has a linear cross section, the bladeconnection portion 6 b has a cross section bent in a zigzag pattern.

Since the cross sectional shape of the blade connection portion 6 bdepicted in FIG. 5 is a same shape as that of the protruding side 6 bsof the blade connection portion 6 b protruding from the sector mold 3,the cross section of the blade connection portion 6 b depicted in FIG. 5is denoted by the reference sign 6 bs of the protruding side.

In the following, in a cross sectional shape of a blade, the referencesign of the protruding side is applied to the cross section of the bladeconnection portion.

The length of the portion of the cross section of the blade connectionportion 6 b that is bent in a zigzag pattern (the sum total of thelength of the protruding side 6 bs of the blade connection portion 6 bin the form of a thin plate protruding from the mold surface 4 f, thelength of a broken line depicted in FIG. 5) is the full length Lc of theprotruding side 6 bs of the blade connection portion 6 b.

The full length Lc of the protruding side 6 bs of the blade connectionportion 6 b is longer by an amount given by the bent portion than theprotrusion distance from the mold surface 4 f.

The full length Lc of the protruding side 6 bs of the blade connectionportion 6 b is a length over which it is embedded in the tire tread 21and becomes resistance when the blade connection portion 6 b is pulledout at the time of mold opening and indicates a degree of difficulty inpullout from the mold, and pullout from the mold becomes easier as thefull length Lc of the protruding side 6 bs of the blade connectionportion 6 b becomes smaller.

The blade distal end side thick portion 6 c has a circular crosssectional shape depicted in FIG. 5, and the diameter of the circularshape is the thickness Wc of the blade distal end side thick portion 6 cexpanded in the thicknesswise direction. In the cross sectional viewdepicted in FIG. 5, the sweep area that is the difference where thesectional area of the blade connection portion 6 b is subtracted fromthe area from the blade distal end side thick portion 6 c to the moldsurface 4 f with a width equal to the maximum width Wc of the thicknessof the blade distal end side thick portion 6 c (area of a portionindicated by a scattered dot pattern in FIG. 5) is represented by Sc.

An enlarged sectional view of a blade 7 in each circumferential endportion side region E is depicted in FIG. 6.

The blade 7 has a blade proximal end portion 7 a to be embedded into thesector mold 3, a blade distal end side thick portion 7 c expanded in thethicknesswise direction on the distal end side, and a blade connectionportion 7 b that connects the blade proximal end portion 7 a and theblade distal end side thick portion 7 c to each other.

The blade proximal end portion 7 a and the blade connection portion 7 bhave a form of a thin plate of a fixed plate thickness and have a linearcross section. The full length of a protruding side 7 bs of the bladeconnection portion 7 b (length of a broken line depicted in FIG. 6) isLe.

The blade distal end side thick portion 7 c has an oval cross sectionalshape depicted in FIG. 6, and the thickness thereof expanded in thethicknesswise direction is We.

In the cross sectional view depicted in FIG. 6, the sweep area that isthe difference where the cross sectional area of the blade connectionportion 7 b is subtracted from the area from the blade distal end sidethick portion 7 c to the mold surface 4 f with a width equal to themaximum width We of the thickness of the blade distal end side thickportion 7 c (area of a portion indicated by a scattered dot pattern inFIG. 6) is represented by Se.

Referring to FIGS. 5 and 6, if the blade 6 in the circumferentialcentral portion side region C of the sector mold 3 and the blade 7 inthe circumferential end portion side regions E are compared with eachother, then the sweep area Sc of the blade 6 in the circumferentialcentral portion side region C and the sweep area Se of the blade 7 inthe circumferential end portion side regions E are substantially equalto each other.

However, the full length Le of the protruding side 7 bs of the bladeproximal end portion 7 a of the blade 7 in the circumferential endportion side regions E is shorter than the full length Lc of thezigzag-patterned protruding side 6 bs of the blade connection portion 6b of the blade 6 in the circumferential central portion side region C(Le<Lc).

By making the full length Le of the protruding side 7 bs of the bladeproximal end portion 7 a of the blade 7 in the circumferential endportion side regions, which blade is not easier in pullout from the moldthan the blade 6 in the central portion side region of the sector mold3, shorter than the full length Lc of the protruding side 6 bs of theblade connection portion 6 b of the blade 6 in the circumferentialcentral portion side region, pullout of the entire sector mold can beperformed smoothly without causing failure at the time of mold openingof the vulcanization mold.

The pneumatic tire 20 manufactured using the vulcanization mold 1 makespullout thereof from the mold at the time of mold opening smooth, andthe manufacturing efficiency can be increased without causing failure inmold pullout such as missing of part of blocks.

Now, a vulcanization mold according to another embodiment is describedwith reference to FIGS. 7 to 9.

The sector molds of the present vulcanization mold have a structure sameas that of the sector molds 3 and same reference signs are applied toboth split molds and circumferential ridges together with the sectormolds.

Similarly, same reference signs are also used for the pneumatic tire andthe tire tread.

On the mold surface 4 f of the sector mold 3, blades 8 and 9 that arethin plate-like members are implanted between adjacent circumferentialridges 5 such that they extend in a rather inclined relationship withrespect to the tire widthwise direction.

FIG. 7 is a cross sectional view perpendicular to the tire widthwisedirection of the sector mold 3 of the present vulcanization mold.

Referring to FIG. 7, blades 8 in the circumferential central portionside region C and blades 9 in the circumferential end portion sideregions E protrude perpendicularly from the mold surface 4 f.

At the time of mold opening, the blades 8 and 9 are pulled out from thetire tread 21 in a radial direction R in which the sector mold 3 ismoved away from the center.

As described hereinabove, in regard to each blade 9 in thecircumferential end portion side regions E of the sector mold 3, theprotruding direction is not parallel to the radial direction R in whichit is pulled out from the tire tread at the time of mold opening but hassome angle. Therefore, since the blade 9 having a blade distal end sidethick portion 9 c tends to be pulled out in the radial direction Rhaving the angle with respect to the protruding direction thereof, it isacted upon by comparatively high resistance, and pullout of the blade 9from the mold is not easy in comparison with that of the blade 8 in thecircumferential central portion side region C.

Therefore, the blades 8 in the circumferential central portion sideregion C and the blades 9 in the circumferential end portion sideregions E have shapes different from each other.

An enlarged cross sectional view of a blade 8 in the circumferentialcentral portion side region C is depicted in FIG. 8.

The blade 8 has a blade proximal end portion 8 a to be embedded into thesector mold 3, a blade distal end side thick portion 8 c expanded in itsthicknesswise direction on the distal end side, and a blade connectionportion 8 b that connects the blade proximal end portion 8 a and theblade distal end side thick portion 8 c to each other.

The blade proximal end portion 8 a and the blade connection portion 8 bhave a form of a thin plate of a fixed plate thickness, and while theblade proximal end portion 8 a has a linear cross section, the bladeconnection portion 8 b has a cross section bent in a zigzag pattern.

The full length of the protruding side 8 bs of the blade connectionportion 8 b, which is bent in the zigzag pattern, of the blade 8 in thecircumferential central portion side region C is Lc.

The full length Lc of the protruding side 8 bs of the blade connectionportion 8 b is longer by an amount given by the bent portion than theprotrusion distance from the mold surface 4 f.

The blade distal end side thick portion 8 c has a circular crosssectional shape depicted in FIG. 8, and the thickness expanded in thethicknesswise direction is Wc.

In the cross sectional view depicted in FIG. 8, the sweep area that isthe difference where the cross sectional area of the blade connectionportion 8 b is subtracted from the area from the blade distal end sidethick portion 8 c to the mold surface 4 f with a thickness equal to themaximum width We of the thickness of the blade distal end side thickportion 8 c (area of a portion indicated by a scattered dot pattern inFIG. 8) is represented by Sc.

An enlarged cross sectional view of a blade 9 in the circumferential endportion side regions E is depicted in FIG. 9.

The blade 9 has a blade proximal end portion 9 a to be embedded into thesector mold 3, a blade distal end side thick portion 9 c expanded in itsthicknesswise direction on the distal end side, and a blade connectionportion 9 b that connects the blade proximal end portion 9 a and theblade distal end side thick portion 9 c to each other.

The blade proximal end portion 9 a and the blade connection portion 9 bhave a form of a thin plate of a fixed plate thickness and have a linearcross section.

The full length of a protruding side 9 bs of the blade connectionportion 9 b (length of a side of the plate connection portion 9 b in theform of a thin plate protruding from the mold surface 4 f, length of abroken line depicted in FIG. 9) is Le.

The blade distal end side thick portion 9 c has a circular crosssectional shape depicted in FIG. 9, and the diameter of the circularshape is a thickness We expanded in the thicknesswise direction of theblade distal end side thick portion 9 c.

In the cross sectional view depicted in FIG. 9, the sweep area that isthe difference where the cross sectional area of the blade connectionportion 9 b is subtracted from the area from the blade distal end sidethick portion 9 c to the mold surface 4 f with a width equal to themaximum width We of the thickness of the blade distal end side thickportion 9 c (area of a portion indicated by a scattered point pattern inFIG. 5) is represented by Se.

As described hereinabove, the sweep area Se is an area over which theblade distal end side thick portion 9 c and the blade connection portion9 b embedded in the tire tread 21 are acted upon by resistance when theyare pulled out at the time of mold opening and indicates a degree ofdifficulty in pullout from the mold. As the sweep area Se decreases,pullout from the mold becomes easier.

Referring to FIGS. 8 and 9, if the blade 8 in the circumferentialcentral portion side region C and the blade 9 in the circumferential endportion side regions E are compared with each other, then the fulllength Le of the protruding side 9 bs of the blade connection portion 9b of the blade 9 in the circumferential end portion side regions E isshorter than the full length Lc of the protruding side 8 bs of the bladeconnection portion 8 b of the blade 8 in the circumferential centralportion side region C. However, the sweep area Se of the blade 9 isgreater than the sweep area Sc of the blade 8, and pullout from the moldis not easy.

Therefore, in the present embodiment, not only the full length of theprotruding side of the blade connection portion but also the sweep areaindicating another degree of difficulty in pullout from the mold aretaken into consideration at the time of design to facilitate pullout ofthe entire sector mold.

In particular, comparing the multiplication value Mc obtained bymultiplying the full length Lc of the protruding side 8 bs of the bladeconnection portion 8 b of the blade 8 in the circumferential centralportion side region C by the sweep area Sc of the blade 8 (Mc=Lc×Sc) andthe multiplication value Me obtained by multiplying the full length Leof the protruding side 9 bs of the blade connection portion 9 b of theblade 9 in the circumferential end portion side regions E by the sweeparea Se of the blade 9 (Me=Le×Se) with each other, the multiplicationvalue Me of the blade 9 in the circumferential end portion side regionsE is made lower than the multiplication value Mc of the blade 8 in thecircumferential central portion side region C (Me<Mc).

As the multiplication value of the full length of the protruding side ofthe blade connection portion of the blade and a sweep area of the bladedecreases, pullout from the mold becomes easier.

Accordingly, by making the multiplication value Me (=Le×Se) of the blade9 in the circumferential end portion side region E, which blade is noteasier in pullout from the mold than the blade 8 in the central portionside region C of the sector mold 3, lower than the multiplication valueMc (=Lc×Sc) of the blade 8 in the circumferential central portion sideregion C, pullout of the entire sector mold can be performed smoothlywithout causing failure at the time of mold opening of the vulcanizationmold.

The pneumatic tire 20 manufactured using the vulcanization mold of thepresent embodiment makes pullout from the mold at the time of moldopening smooth, and the manufacture efficiency can be increased withoutcausing mold pullout failure such as missing of part of blocks.

Although the vulcanization molds of the two embodiments according to thepresent invention have been described, the mode of the present inventionis not restricted to the embodiments described above, and the presentinvention includes what are carried out in various modes withoutdeparting from the subject matter of the present invention.

For example, although the shapes of the blades of the present inventionare not restricted to those of the blades disclosed by the embodimentsand various shapes are applicable, it is sufficient only if the bladessatisfy the requirements of claim 1.

Especially, the cross sectional shape of the blade distal end side thickportion is not restricted to a circular shape or an oval shape, andvarious shapes such as a triangular shape that is a flask shape andother polygonal shapes are applicable.

It is to be noted that the blade distal end side thick portion is athick portion existing on the distal end side of the blade but does notnecessarily exist at the distal end of the blade, and may have such ashape that the thickness decreases from the thick portion toward theinner side in the diametrical direction.

Further, the full length of the protruding side of the blade connectionportion or the multiplication value of the blades implanted to the moldsurface of the sector mold may be set so as to gradually decrease fromblades at a central portion in the circumferential direction to bladeson end portion sides in the circumferential direction.

Further, the grooves formed by the blades are not limited to the sipesthat are narrow grooves and also include rather wide widthwise groovesextending in the tire widthwise direction.

Furthermore, although the number of circumferential ridges in theembodiments described hereinabove is five, the number of circumferentialridges is not limited to five and may be greater or smaller than five.

REFERENCE SIGNS LIST

-   -   1: Vulcanization mold    -   2: Holder    -   3: Sector mold    -   4: Split mold    -   4 f: Mold surface    -   5: Circumferential ridge    -   6: Blade    -   6 a: Blade proximal end portion    -   6 b: Blade connection portion    -   6 bs: Protruding side    -   6 c: Blade distal end side thick portion    -   7: Blade    -   7 a: Blade proximal end portion    -   7 b: Blade connection portion    -   7 bs: Protruding side    -   7 c: Blade distal end side thick portion    -   8: Blade    -   8 a: Blade proximal end portion    -   8 b: Blade connection portion    -   8 bs: Protruding side    -   8 c: Blade distal end side thick portion    -   9: Blade    -   9 a: Blade proximal end portion    -   9 b: Blade connection portion    -   9 bs: Protruding side    -   9 c: Blade distal end side thick portion    -   20: Pneumatic tire    -   21: Tire tread    -   25: Tire circumferential groove    -   26: Sipe    -   27: Sipe    -   C: Circumferential central portion side region    -   E: Circumferential end portion side region    -   Sc, Se: Sweep area    -   Lc, Le: Full length of protruding side of blade connection        portion

1. A vulcanization mold in which an annular mold for forming a tiretread of a pneumatic tire is split in a circumferential direction into aplurality of sector molds and the sector molds are each moved indirections toward a center and combined with each other to clamp a rawtire on an inner side to vulcanization mold the raw tire, each of thesector molds having blades implanted on a mold surface thereof, theblades being thin plate-like members extending in a tire widthwisedirection and being used to form groove lines on the tire tread, each ofthe blades having a blade proximal end portion to be embedded into thesector mold, a blade distal end side thick portion expanded in athicknesswise direction on the distal end side, and a blade connectionportion that connects the blade proximal end portion and the bladedistal end side thick portion to each other, wherein a full length of aprotruding side that protrudes from the sector mold of the bladeconnection portion of the blade is shorter at the blades in thecircumferential end portion side regions than at the blades in thecircumferential central portion side region of the sector mold.
 2. Thevulcanization mold as claimed in claim 1, wherein a multiplication valueobtained by multiplying a sweep area that is a difference where a crosssectional area of the blade connection portion is subtracted from anarea from the blade distal end side thick portion to the mold surfacewith a width equal to a maximum width of a thickness of the blade distalend side thick portion in a cross sectional shape perpendicular to thetire widthwise direction of the blade by a full length of a protrudingside of the blade connection portion is smaller at the blades in thecircumferential end portion side regions than at the blades in thecircumferential central portion side region of the sector mold.
 3. Apneumatic tire manufactured using the vulcanization mold according toclaim
 1. 4. A pneumatic tire manufactured using the vulcanization moldaccording to claim 2.